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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Life history of capelin (Mallotus Villosus (Müller, 1776)) and dietary overlap with Arctic cod (Boreogadus saida (Lepechin, 1774)) in the Canadian Arctic

McNicholl, Darcy, McNicholl, Darcy 27 November 2015 (has links)
Capelin (Mallotus villosus (Müller, 1776)) is an important marine forage fish species that typically inhabits sub-Arctic and temperate circumpolar waters. Capelin have recently been reported in greater abundance in Arctic regions, and are considered an indicator for warming climate in the northern marine ecosystem. The goal of this thesis is to examine intrinsic factors among capelin populations, and whether niche overlap among sympatric capelin and Arctic cod (Boreogadus saida (Lepechin, 1774)) will affect the abundance and persistence of capelin in the Arctic as temperatures continue to rise. Life history comparisons of capelin from two Arctic regions (Western Beaufort Sea, Cumberland Sound) relative to a sub-Arctic population (Newfoundland) show that body size, body condition, growth rate and age-at-maturity vary among these regions. Life history characteristics that are adapted to northern environments and increasing temperatures will allow the presence and persistence of this species to increase in the Arctic. The consequence of increased abundance of capelin in the Arctic environment could be competition between capelin and Arctic cod, an Arctic species within a similar dietary niche. Stomach contents indicated that both species feed primarily on calanoid copepods and this result was corroborated with high dietary overlap in isotopic bivariate space (carbon and nitrogen stable isotopes). The occurrence of capelin is expected to increase in the Arctic with rising temperatures, thus adaptation in life history traits in capelin specific to each region may facilitate increased abundance and persistence, and possibly contribute to competitive pressure on Arctic cod. Potential competition will be particularly important in nearshore and shelf habitats where shifts in availability of intermediate trophic level taxa will influence diet and distribution of key predators such as beluga, sea birds, and anadromous fishes. As the Arctic environment changes with climate shifts, newly adapted or dispersed species from sub-Arctic systems are expected to drive shifts in ecosystem structure and function in the marine environment. / October 2016
32

Observations on the Life History of the Brown Spider, Loxosceles Reclusa Gertsch and Muliak

Horner, Norman 08 1900 (has links)
This research was undertaken primarily to further elucidate the life history of this medically important spider. Special attention was given to rearing experimental spiders under as near-natural environmental conditions as possible.
33

Effects of hybridization and life history tradeoffs on pathogen resistance in the Harvester ants (Pogonomyrmex)

Hernaiz-Hernandez, Yainna M. 01 January 2015 (has links)
A fundamental challenge faced by all organisms is the risk of infection by pathogens that can significantly reduce their fitness. The evolutionary dynamic between hosts and pathogens is expected to be a coevolutionary cycle, as pathogens evolve by increasing their level of virulence and hosts respond by increasing their level of resistance. The factors that influence the dynamics of adaptation by pathogen and host in response to one another are not well understood. Social insects live in dense colonies in high-pathogen soil environments, making them an ideal model system to study the factors influencing the evolution of pathogen resistance. In this thesis work, I investigated several alternative hypotheses to explain patterns of host resistance to entomopathogenic fungi in the harvester ant genus Pogonomyrmex: that high resistance is associated with high environmental pathogen loads, that local adaptation leads to increased resistance to coevolved pathogen populations, that life history tradeoffs increase allocation to resistance in harsher environments, and that increased genetic diversity caused by interspecific hybridization enhances inherent resistance. First, I characterized patterns of spatial variation in abundance and diversity of fungal pathogens among habitats of Pogonomyrmex species. I found 17 genera of fungi in the soil, six of which were entomopathogenic. Lower precipitation habitats, where P. rugosus occurs, had the lowest diversity, while the highest was experienced by the H lineage, one of two hybrid populations. When actual infection rates of field-caught workers were compared, the mesic-habitat P. barbatus was infected significantly more often. These results suggest that habitat does plays a role in fungal diversity, and that species are exposed to more entomopathogens may be more likely to get infected. Second, I tested experimentally whether hybridization and or habitat differences play a role in pathogen resistance by testing the effect of soil type and species identity on infection rates in pupae of the two species and their hybrids. This experiment showed P. rugosus ants had the highest inherent resistance to infection, supporting the life history tradeoff hypothesis. This suggest that Pogonomyrmex ants species are allocating their resources differently according to their environment, with more stressful environment leading to less investment in reproduction and more in protection against pathogens. Overall our study shows that environment plays a role in differences in infection risk, while genetic effects such as hybridization may not play a role in pathogen resistance.
34

Substance, History, and Politics

Black, Candace J., Figueredo, Aurelio José, Jacobs, W. Jake 01 1900 (has links)
The aim of this article is to examine the relations between two approaches to the measurement of life history (LH) strategies: A traditional approach, termed here the biodemographic approach, measures developmental characteristics like birthweight, gestation length, interbirth intervals, pubertal timing, and sexual debut, and a psychological approach measures a suite of cognitive and behavioral traits such as altruism, sociosexual orientation, personality, mutualism, familial relationships, and religiosity. The biodemographic approach also tends not to invoke latent variables, whereas the psychological approach typically relies heavily upon them. Although a large body of literature supports both approaches, they are largely separate. This review examines the history and relations between biodemographic and psychological measures of LH, which remain murky at best. In doing so, we consider basic questions about the nature of LH strategies: What constitutes LH strategy (or perhaps more importantly, what does not constitute LH strategy)? What is gained or lost by including psychological measures in LH research? Must these measures remain independent or should they be used in conjunction as complementary tools to test tenets of LH theory? Although definitive answers will linger, we hope to catalyze an explicit discussion among LH researchers and to provoke novel research avenues that combine the strengths each approach brings to this burgeoning field.
35

Adaptation and Diversification in Bluebells (Mertensia spp., Boraginaceae)

Lin, Shang-Yao Peter 06 June 2019 (has links)
Examining the ecological processes generating evolutionary patterns is crucial to understanding how biodiversity arises and evolves. One of the most striking examples of evolutionary diversification is provided by the flowering plants (angiosperms) and their flowers. Pollinators are traditionally considered to be the most important selective agents and drivers of floral diversity. However, many angiosperms have a generalized floral morphology and are visited by a diverse and overlapping suite of pollinators, making it unclear how pollinators could have driven diversification in these taxa. In addition, flowers and plant reproductive success are likely to be influenced by factors other than pollinators, such as herbivores, precipitation, and temperature. These factors need to be considered along with pollinators in order to improve our understanding of angiosperm evolution and diversification. In my thesis, I focussed on the processes influencing adaptation and diversification in flowering plants in the genus Mertensia (Boraginaceae), which have relatively unspecialized flowers that attract a variety of nectar- and pollen-feeding insects. In Chapter One, I explored correlations among floral traits, vegetative traits, and flowering phenology across 12 Mertensia species. In Chapter Two, I assessed reproductive isolating barriers between related Mertensia species occurring in sympatry. In Chapter Three, I examined the ecological function of floral orientation in two Mertensia species with respect to pollinators and precipitation. First, across Mertensia species, I found that early-flowering species were shorter, produced fewer flowers, and occurred at higher altitudes than late-flowering species—suggesting a life-history trade-off between plant size and flowering phenology, as well as an altitudinal effect on both traits. Interspecific variation in floral traits was not strongly associated with variation in flowering phenology or plant size. Second, between sympatric M. brevistyla and M. fusiformis populations, I found weak reproductive isolating barriers and possible hybridization. Most pre-pollination barriers were weak, as the two Mertensia species shared similar habitats, flowering phenology, and pollinator assemblages. The two relatively strong barriers were floral (ethological and mechanical) isolation and post-pollination isolation: Pollinators transferred significantly more of a pollen analogue among conspecific than heterospecific plants in mixed-species arrays, and flowers yielded higher seed set when receiving conspecific rather than heterospecific pollen in hand-pollination experiments. Lastly, I found that floral orientation was more likely to be under selection by precipitation than by pollinators, in that paternal fitness (i.e., pollen germination) was reduced by contact with water and that pollinator-mediated selection via maternal fitness (i.e., seed set) was not detected. A more pendant floral orientation likely protects the relatively long and exposed anthers of M. fusiformis from rain, while the less pendant M. brevistyla does not require this protection because of its shorter, more concealed reproductive structures. Although I detected an effect of floral orientation on seed set, I was not able to identify the selective agents driving this effect. In summary, my results suggest that pollinators play a minor role in influencing floral adaptation and diversification in Mertensia. Instead, the dominant influences on the traits I examined appear to be life-history trade-offs, environmental conditions that vary along altitudinal gradients, and abiotic variables (e.g., precipitation). It is important to consider these factors and their influences on paternal and maternal fitness in order to gain a broader perspective on floral evolution in plants with generalized pollination systems.
36

Juggling identities : elite female athletes' negotiation of identities in disability sport

Seal, Emma January 2015 (has links)
The focus of this thesis is the negotiation of identities by elite-level female athletes involved in disability sport. Recently, the London 2012 and Sochi 2014 Paralympic games have showcased the contemporary nature of disability sport and ostensibly suggest a growth in public interest within this field. However, there has been limited research to date conducted into the experiences of physically impaired, female athletes at the elite level of disability sport. Moreover, the existing literature fails to address the negotiation of identities within the interplay of gender, ‘disability’, body and wider socio-cultural influences. Inspired by this dearth of literature and the desire to contribute to disability sport theorisation, my research questions how elite female athletes negotiate their identities across contexts and the wider social, cultural and political values that influence this process. I address their experiences in relation to these factors alongside the intersection of gender and disability. I have explored the women’s experiences by utilising symbolic interactionism in combination with a social-relational conceptualisation of disability. This theoretical approach recognises the women’s bodies as a ‘fleshy presence’ in their interactional encounters and brings ‘impairment’ back into the theorisation of disability (Waskul and Vannini 2006). This approach allows me to interrogate the women’s unique realities in relation to wider socio-cultural values, and the ‘micro relations’ of their day-to-day lives. A life history perspective guides the methodological framework, which foregrounds and prioritises the seven elite female athletes’ subjective experiences in relation to the socio-historical context. The narratives offer a powerful and original insight into the complexity of disability, whilst addressing the multiple and fluid nature of the participants’ identities. This advances the use of the social-relational model and fosters new understandings of the social relations underpinning the effects of impairment. I have developed the concept of ‘reverse stigma’ and have highlighted the need to disrupt the social processes that create stigmatic physicality, whilst demonstrating how impairment is perceived in different social contexts. My research has provided an original contribution by generating an in-depth picture of how the women experience their lives, how they see themselves as disabled (or not) and the wider intersecting forces that shape and influence their realities. This is significant for highlighting the way disability and disabled female athletes are perceived in Western society.
37

Aspectos evolutivos da história de vida e estrutura da casca do ovo de lagartos tropiduríneos / Evolutive aspects of life history and eggshell morphology of Tropidurinae lizards

Nunes, Renata Brandt 27 August 2010 (has links)
Em lagartos, componentes de história de vida apresentam grande plasticidade fenotípica e evoluem de maneira correlacionada. O número de ovos, por exemplo, tende a ser correlacionado positivamente com o tamanho corpóreo das fêmeas grávidas, tanto em linhagens evolutivas quanto entre indivíduos, embora alguns tipos de hábito pareçam restringir ninhadas maiores. Há indícios de que outros fatores, como componentes climáticos, ou latitude, também sejam determinantes das características de história de vida do grupo, tanto por questões de fisiologia termal quanto ecológicas. Componentes climáticos influenciam ainda diferentes aspectos da reprodução em lagartos, como por exemplo a estrutura e morfologia da casca dos ovos de Squamata, conforme indicam diferenças nestas características entre linhagens de lagartos ovíparos. Neste contexto, o presente trabalho investigou aspectos evolutivos da história de vida de lagartos da subfamília Tropidurinae, e sua relação com componentes climáticos e latitude, através de métodos filogenéticos comparativos. Observou-se que o número de ovos da ninhada é positivamente correlacionado com o tamanho corpóreo ao longo da linhagem dos tropiduríneos. Por outro lado, esse padrão não é observado no caso de hábito escansorial e utilização de frestas de rochas, em razão de possíveis compromissos envolvendo peso e forma corpórea com efeitos na sobrevivência das fêmeas. O tamanho corpóreo em tropiduríneros é maior em regiões geográficas com maiores componentes de precipitação, possivelmente relacionado a disponibilidade de alimento. Há diminuição do tamanho corpóreo com incrementos na distância da linha do Equador, até aproximadamente 1500 km. A partir desse limite, o tamanho corpóreo aumenta. Adicionalmente foi estudada a morfologia e estrutura da casca de Tropidurus torquatus, uma das espécies com distribuição mais ampla dentro da subfamília. A morfologia da casca de Tropidurus torquatus segue o padrão geral para Squamata com algumas particularidades, mas estudos comparativos futuros é que elucidarão padrões evolutivos da morfologia da casca. / In lizards, life history components have great phenotypic plasticity and evolve in a correlated way. Clutch size, for example, tends to be positively correlated to body size of gravid females, when comparing different evolutive lineages or different individuals, though some kinds of habit seems to restrict larger clutches. There are indications that other factors, such as climate components or latitude, also determine characteristics of lizard life history, as a matter of thermal physiology or ecology. Climate factors also affect different aspects of lizards reproduction, for example the structure and morphology of Squamata eggshells, as differences observed in these factors between oviparous lizards lineages indicate. In this context, the present work investigated evolutive aspects of Tropidurinae lizards life history and its relation to climate components and latitude, using comparative phylogenetic methods. It has been observed that clutch size is positively correlated to body size in the Tropidurinae lineage. On the other hand, this pattern is not observed in lizards with scansorial habits or those that inhabit rock crests, maybe due to compromises involving the weight and shape of female bodies that can affect female survival. The body size in Tropidurinae is larger in geographical regions presenting higher precipitation, possibly due to increased food availability. Female body size decreases with increased distance from the Equator until approximately 1500 km. Beyond this limit, female body size increases. Additionally, morphology and structure of eggshells were studied on Tropidurus torquatus, one of the species within the Tropidurinae group with higher latitudinal range of distribution. Tropidurus torquatus eggshell morphology follows the general pattern described for Squamata with some particularities, and future comparative studies are needed to elucidate evolutive patterns of eggshell morphology in the group.
38

Bahraini Muslim women and higher education achievement : reproduction or opportunity?

Beckett-McInroy, Clare Elizabeth January 2006 (has links)
This research compares and contrasts the life histories of eleven Bahraini Muslim women, aged between twenty five and fifty, who are educationally ‘successful’, defined as having one or more university degree. It analyzes their educational experiences to see if theories of social reproduction apply to their lives. To this end, the work of Pierre Bourdieu and his concept of cultural capital in its institutionalized, objectified and embodied states are applied, where possible, to the women’s life histories, in particular their educational experiences and related areas. This work shows that embodied cultural capital plays a part in the educational success of the women involved in this study, regardless of social class. For some of the women, institutionalized and objectified cultural capital also played a part and the women who possess these tend to come from more affluent families. It also appears that significant others and critical incidents influence their educational successes. Significant others are those people who have encouraged them educationally in different ways: critical incidents include such things as government scholarships for university degree courses within Bahrain and abroad. Having these things may help other Bahraini Muslim women achieve educational ‘success’. Additionally, the women’s innate ability, their ability to juggle their many life projects and roles, other forms of capital (especially economic capital), their marital status, religious obligations and their culture, all influence their educational choices.
39

The ecology of ageing in albatrosses

Froy, Hannah January 2014 (has links)
Age-related variation in demographic rates has significant consequences for population and evolutionary dynamics, and understanding the processes driving such variation is therefore an important aspect of evolutionary ecology. Reproductive performance may vary over the lifetime of an individual, and this may be the result of both variations in reproductive effort and changes in individual competency. For example, increasing experience is likely to have beneficial effects on reproduction during early life, and senescence, or declines in physiological function, may have negative impacts on the performance of older individuals. The rate at which these changes occur can vary dramatically between species, and even between individuals of the same species. However, understanding the causes and consequences of this variation in the rate of ageing is not always straightforward. As well as the individual-level processes described, the phenotypic composition of successive age classes will contribute to age-related variation observed at the population level. Abrupt changes in performance, such as the poor performance of first time breeders, may be obscured if individuals vary in their age at first reproduction. Population-level patterns may also be influenced by selection; for example, the selective disappearance of low quality individuals from older age classes may mask senescent declines in the performance of longer-lived individuals. Moreover, the physiological mechanisms that underpin within-individual changes in performance are not well understood. Unravelling the drivers of such age-related variation requires longitudinal data, following individuals throughout their lives, which presents challenges for the study of natural populations. Albatrosses are among the longest lived vertebrates. In this thesis, I use data from three species of albatross breeding at Bird Island, South Georgia (54°00’S, 38°03’W) to explore age-related variation. Focusing primarily on the wandering albatross, Diomedea exulans, I characterise the relationship between age and various reproductive traits, and decompose the population-level patterns to reveal effects of experience, senescence and terminal effects across the reproductive lifespan of individuals. I then consider foraging behaviour as a proximate driver of changes in reproductive performance in this species. Using tracking data collected over a 20 year period, I find limited evidence for age-related variation in foraging trips taken throughout the breeding cycle. Going one step further, I explore telomere dynamics in the wandering albatross, examining the potential for telomere length to act as a physiological marker of individual state. Finally, I move on to a species comparison, incorporating data from the black-browed (Thalassarche melanophris) and grey-headed albatross (Thalassarche chrysostoma). I compare the population- and individual-level ageing patterns of these three closely related species, and consider these in light of their differing life history strategies.
40

Evolutionary ecology of transmission strategies in protozoan parasites

Pollitt, Laura C. January 2011 (has links)
In recent years there has been growing interest in applying frameworks from evolutionary ecology to understand infectious disease. It is becoming increasingly apparent that the interactions between parasites within the host environment can shape parasite phenotypes underlying infection dynamics and transmission. However, the spread of the disease will crucially depend on both within-host and between-host dynamics. Bridging these scales is challenging and for vector borne parasites, such as malaria and trypanosomes, will involve gaining a much better understanding of infection dynamics both within the host and vector. I apply evolutionary ecology frameworks including social evolution, life history theory, and phenotypic plasticity to investigate how parasite phenotypes are shaped by within-host and within-vector environments and examine the implications for inhost survival and between-host transmission. Specifically, I demonstrate that; 1. Within the host; i. In accordance with theory malaria parasites detect and respond to the presence of competitors by altering reproductive strategies to maximise in-host survival. Furthermore, these strategies are fine tuned in response to variation in the within-host environment, including the availability of resources. ii. The reproductive investment strategies of malaria parasites can be applied to explain the transmission strategies of African trypanosomes. This shows how general evolutionary frameworks can be applied to a novel parasite species and demonstrates the explanatory power of an evolutionary approach. iii. The complexity of the within-host environment poses specific statistical challenges for examining the temporal dynamics of parasite life history traits that are often not adequately dealt with, potentially leading to type 1 errors. Methods to evaluate levels of autocorrelation and how to deal with it are applied to datasets of within-infection dynamics. 2. Within the vector; i. Malaria parasites undergo programmed, apoptotic cell death. The occurrence of, and putative explanation for, apoptosis in protozoan parasites is controversial. I demonstrate the importance of quantitative methods and parasite ecology in testing the evolutionary explanations for parasite apoptosis. ii. The links between within-host dynamics and within-vector dynamics are complex and can lead to counter-intuitive implications for the success of between-host transmission. Density-dependent processes result in diverse fitness costs to parasites of crowding. More broadly, these processes could explain why parasites undergo apoptosis. In general my results demonstrate, across vertebrate hosts and insect vectors, how the interactions between parasites and with their environment shapes traits important for the transmission of infectious disease.

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